EP 263 378 describes transparent blends of BPA polycarbonate and polymethyl methacrylate (PMMA) of which the production is dependent on special parameters, such as the molecular weight of the components, the process used to produce the PMMA, temperature, etc. In Abstracts of the 6th Annual Meetings, Polymer Processing Society, in Nizza (France), D. R. Paul et al. show that, in principle, blends of BPA polycarbonate and PMMA are only single-phase and transparent when produced from solution. The blends undergo phase separation on heating, as described by the lower critical solution temperature (LCST) which, in turn, is below the temperatures normally applied in the thermoplastic processing of BPA polycarbonate blends (T&gt;220.degree. C.). Accordingly, if BPA polycarbonate and PMMA are mixed in the melt (for example by melt compounding in mixing units, such as kneaders or extruders) only opaque phase-separated blends are obtained. If the individual components have the molecular weights relevant for industrial use, the blend cannot be thermoplastically processed without separation of its individual components.
The above-cited DE-OS 3,901,030 describes not only vinyl polymers containing oxetane groups, but also blends thereof with other thermoplastic polymers or with graft polymers. The use of such blends for the production of optical storage media is neither discussed in nor obvious from the DE-OS.
DE-OS 4,000,233 describes blends of polycarbonates, graft polymers and, optionally, thermoplastic vinyl polymers which contain 0.05 to 5% by weight structural elements (Ia) based on the overall effect. Due to the presence of the graft polymers, the blends are not transparent and are therefore unsuitable for optical storage media.
DE-OS 2,658,849 describes polycarbonates containing additions of polymeric oxetanes in quantities of 0.01% by weight to 5.0% by weight (claim 2 of the DE-OS) or 0.01% by weight to 0.50% by weight (page 6 of the DE-OS). However, the polymeric oxetanes have a different structure and are intended to improve the resistance of the polycarbonates to oxidation and hydrolysis.
In addition, it was known from DE-OS 2,510,463 that plastics can be stabilized by oxetane compounds in combination with phosphites.
The plastics used are of various types (page 7 of the DE-OS). Polycarbonates stabilized in this way are particularly suitable for use in the optical field (page 9 of the DE-OS). The stabilizer is used in a quantity of 0.01 to 1% by weight in admixture with phosphite.
In addition, it is known from DE-OS 2,255,639 that thermoplastic polycarbonates can be stabilized against thermal aging by phosphites containing oxetane groups. The phosphites are used in quantities of 0.01 to 0.2% by weight.
In our opinion, the subject of the present invention is also not obvious from the last three German Offenlegungsschrifts because structurally different oxetanes are incorporated in different quantities in the polycarbonates.
Thermoplastic polycarbonates based on 2,2-bis(4-hydroxyphenyl)-propane (bisphenol A) are those containing quantities of 100 mol-% to 55 mol-%, preferably 100 mol-% to 70 mol-% and, more preferably, 100 mol-% 2,2-bis-(4-hydroxyphenyl)-propane and complementary molar quantities of 45 mol-% to 0 mol-%, preferably 30 mol-% to 0 mol-% and, more preferably, 0 mol-% other diphenols than 2,2-bis-(4-hydroxyphenyl)-propane in uncondensed form, 1,1-bis-(4-hydroxyphenyl)cyclohexane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethyl cyclohexane being preferred.
The polycarbonates based on bisphenol A to be used in accordance with the invention (component A) have molecular weights Mw (weight average, as determined by gel chromatography after preliminary calibration) of 10,000 to 200,000 g/mol and preferably 12,000 to 100,000 g/mol.
The resin-like vinyl polymers used in accordance with the invention as component B) are prepared in accordance with DE-OS 3,901,030 from monomers corresponding to formula ##STR4## in which R.sup.1 is H, CH.sub.3,
In a preferred embodiment,
Up to 30% by weight, preferably up to 20% by weight and, more preferably, up to 10% by weight other vinyl monomers are. optionally copolymerized'. The structural units corresponding to formula (I) are thus present in the vinyl polymers of component B) in quantities of 100% by weight to 70% by weight, preferably in quantities of 100% by weight to 80% by weight, more preferably in quantities of 100% by weight to 90% by weight and, most preferably, in quantities of about 100%, by weight, based on the total weight of component B).
The other vinyl monomers are preferably aromatic vinyl compounds and acrylates and methacrylates other than those corresponding to formula (I) such as for example styrene, .alpha.-methyl styrene, acrylates, methacrylates, preferably styrene, .alpha.-methyl styrene, methyl methacrylate, cyclohexyl methacrylate and phenyl methacrylate.
In connection with component B) "resin-like" means that the polymers are uncrosslinked, have softening temperatures above 30.degree. C. and are thermoplastically processable. The vinyl polymers may be produced from the monomers by known methods of polymerization, preferably in organic solvents or in aqueous suspension or emulsion by radical or thermal polymerization. The polymerization process applied must ensure that the oxetanyl groups remain intact (for example, strongly acidic (pH&lt;1) and strongly alkaline (pH&gt;12) media in conjunction with relatively high temperatures must be avoided in emulsion polymerization)
The molecular weight of the vinyl polymers may be influenced in the usual way through the polymerization temperature, the concentration of monomers, the quantity of catalyst and through molecular weight regulators, preferably organosulfur compounds, for example mercaptans or disulfides, more particularly long-chain mercaptans, such as n- and tert. dodecyl mercaptan. The regulators are normally dissolved in the monomer mixture.
The molecular weights Mw (weight average) of the vinyl polymers are preferably in the range from 3,000 to 800,000 g/mol and more preferably in the range from 10,000 to 500,000 g/mol (as determined by light scattering or sedimentation).
The monomers corresponding to formula (1) are known from the literature (see U.S. Pat. No. 3,105,838) and may be produced by methods known from the literature.
The replacement of bisphenol A by other bisphenols in the polycarbonate A) and the use of other vinyl monomers than those corresponding to formula (I) for the production of B) are critical. The effect of both variants can be that the mixtures of A) and B) are no longer compatible. The effect depends upon the type of the substituted units and their percentage content in the polymer, upon the composition of the other components according to the invention and also upon the mixing ratio of A) and B). In critical cases, therefore, the composition of components A) and B) has to be selected, optionally through reduction of the percentage content of the particular substituting monomers, so that a compatible (single-phase) blend is obtained by melt compounding. The presence of a compatible blend can be verified, for example, by determination of the glass temperature, for example by DSC measurements.
The blends according to the invention of A)+B) and, optionally, C) may also be produced by mixing of solutions of the individual components in a suitable solvent for components A), B) and, optionally, C) and subsequent precipitation or evaporation. Suitable solvents are in principle any solvents which dissolve components A) and B) more particularly methylene chloride and tetrahydrofuran.
In one preferred method of producing the polymer blends according to the invention, the polymers are mixed in the melt at temperatures above 200.degree. C. and preferably at temperatures above 220.degree. C. Mixing may be carried out in typical mixing units, such as mixing rolls, kneaders, single-screw or multiple-screw extruders.
Accordingly, the present invention also relates to a process for the production of the blends according to the invention of components A) and B) and, optionally, C), characterized in that either a) components A) and B) and, optionally, C) are mixed via their solutions and the solution obtained is evaporated in known manner and the mixture is isolated or b) components A) and B) and, optionally, C) are mixed in the melt at temperatures above 200.degree. C. and preferably at temperatures above 220.degree. C. in standard mixing units and the resulting mixture is subsequently melt-compounded or melt-extruded.
The polymer blends are suitable for the production of moldings of all kinds by thermoplastic processing methods, such as extrusion or injection molding. The polymer blends may be used, for example, for the production of optical disks.
Accordingly, the present invention also relates to the use of the blends according to the invention of components A) and B) and, optionally, C) for the production of optical storage media, more particularly optical disks.